Load carrying skeletal members such as the human hip are frequently rendered non-functional because of arthritis, fracture, damage, disease, resections for malignancy or disease, or because of pain or malformation. Such members are commonly repaired by total joint replacement with artifical components, and one type of bone replacement that has been particularly successful over the past 22 years is that of the human hip. Such hip prostheses typically include a metal femoral portion or component which is implanted in the femur and a plastic acetabular component which is secured to the pelvis. The femoral component generally is formed in one piece and includes a stem, a collar, a neck and a head. The stem is adapted to be inserted into the medullary canal of a femur bone while the collar is adapted to rest on the cortical bone in the region of the femoral neck. The head is disposed on the end of the neck and is adapted to rotate within the acetabular component. Cement is most commonly used for implanting the stem in the femur, and examples of femoral components constructed to be cemented into the femur are illustrated in U.S. Pat. Nos. 3,744,061; 4,012,796; 4,146,936; 4,156,943; 3,808,606; 3,102,536; and 4,080,666.
Although many of the hip replacement prostheses described in the aforementioned patents have been used successfully, one significant complication which has developed with almost every known cemented replacement is the high rate of loosening thereof. Various reports of long term results of cemented total hip replacements with a minimum followup of 10 years show that the loosening rate on the femoral side is in the neighborhood of 30 to 50 percent. One reason for the reported high rate of loosening in cemented implants is the weakening or loss of strength of the cement bond resulting from use, which constitutes one primary weakness in the implant. If the cement strength, or the life of the cement bond between the implant and the femur could be increased, the life span of the implant would be significantly increased.
A methylmethacrylate cement is commonly used for cementing such stemmed components into the femur and for cementing acetabular components into the acetabulum. This cement typically consists of a powdered polymer and a liquid monomer which must be mixed together prior to use for polymerization to occur. This mixing is commonly done in a open bowl by hand and produces a gas which is partially released into the atmosphere and which remains partially within the polymerized cement to form bubbles therein. Also, air is drawn into the cement by the mixing process to form pores or bubbles. These bubbles produce a hardened cement having a high porosity.
In addition, this cement is typically injected into the bone cavity using a hand held and operated caulking gun, or syringe after it has been hand mixed in a separate container and hand poured into the gun. This whole process is very awkward because of the large number and variety of implements required and it can be very time consuming.